This invention relates to a noise cancelling device by the use of an adaptive filter.
A noise cancelling device of the type described, is supplied with an input signal having a main signal of for example, a speech signal and a noise signal acoustically superposed on the main signal. The noise cancelling device is for cancelling the noise signal from the input signal.
A background noise component which is superposed on the speech signal supplied through a microphone or a handset results in a serious problem in a speech processing device such as a narrow-band speech encoding unit of a high information compression type or a speech recognition unit. As a noise cancelling device for cancelling the noise component acoustically superposed, proposal is made of a two-input noise cancelling device using an adaptive filter in, for example, an article which is contributed by B. Widrow et al to Proceedings of IEEE, vol. 63, No. 12, December, 1975, pages 1692-1716 (hereinafter "Reference 1").
As will later be described, such a conventional noise cancelling device is incapable of achieving a reduced convergence time and a reduced final residual error after convergence.